Flavour compositions (commonly also known as flavours) contain at least two different sensorially active substances such as, for example, synthetic, natural or nature-identical aromatic substances or plant extracts. Mostly, however, flavours are complex mixtures of many sensorially active components. The sensorially active substances can be volatile (odorous or aromatic substances) or non-volatile (flavouring substances). Volatile aromatic substances can be perceived by human beings both orthonasally and retronasally. Flavouring substances interact with the flavour receptors on the tongue and are responsible for the gustatory (taste) impressions sweet, sour, bitter, salty and umami; in addition, other, often trigeminal stimuli, such as e.g. pungent, burning, cooling, tingling or prickling effects, are also perceived. The proportions of the sensorially active substances in a flavour composition can vary enormously and they naturally have a strong influence on the overall sensory impression of the flavour composition. It is not the absolute amount of a sensorially active component in a flavour which is decisive, but its sensory contribution. Many sensorially important components in foodstuffs are not even known yet, since they are contained in only very small amounts, even though because of their high sensory activity they make a significant olfactory and/or gustatory contribution. More meaningful than the simple amount is therefore the so-called odour activity value, which is defined as the quotient of the concentration of a sensorially active component and its olfactory or gustatory threshold value.
It is often desirable to determine the sensorially active constituents of a flavour composition and to this end to fractionate the flavour composition in order to develop new gustatorily attractive flavour compositions and also for quality control purposes in the production of flavour compositions. The sensory evaluation of the individual fractions is conventionally carried out by means of dilution analysis. An overview of this topic can be found in Chemie in unserer Zeit 2003, 37, 388-401 and in the literature cited therein.
A conventional fractionation process is high-performance liquid chromatography (HPLC). A further development of HPLC is high-temperature liquid chromatography (HTLC), in which temperature-programmable HPLC ovens and temperature-stable HPLC columns are used. The person skilled in the art can find an overview of HTLC in the publication LABO (Magazin für Labortechnik & Life Sciences), March 2004 edition, 19-22.
In GC/olfactometry, a mixture of odorous, volatile components is separated by gas chromatography and the olfactorily relevant components are inhaled through the nose at a gas outlet from the gas chromatograph in carrier gas and ambient air and are olfactorily evaluated; the perception is thus exclusively orthonasal. An overview of this can be found for example in the monograph “ACS Symposium Series 782, Gas Chromatography—Olfactometry”, Oxford University Press, 2001.
In JP 09-248164 (Hitachi Zosen Corp.) the flavour of tea extracts is determined by means of HPLC analysis. The ratios of the peak areas of certain sensorially active components serve as a quality standard for the flavour of the tea. A mixture consisting of water, 13% methanol and 0.1% phosphoric acid was used as the mobile phase for the HPLC method performed therein. The process conditions for the HPLC separation, the way in which the eluted fractions are freed from methanol and the procedure for sensory evaluation are not described in any further detail.
In customary HPLC separating processes for the analysis of flavour compositions, mobile phases (eluents) are conventionally used which are miscible with water but which are organic and harmful or toxic solvents. Commonly used eluents are acetonitrile, methanol and tetrahydrofuran as well as mixtures thereof with water or aqueous buffers. The harmful solvents must be removed from an eluted fraction before a sensory evaluation. This removal requires the use of time-consuming, mostly thermal or extractive processes such as distillation or freeze-drying, for example. These processes often result in a change in the composition of the flavouring and aromatic substances contained in the eluted fraction, due in particular to thermal and/or oxidative influences. Accordingly, the sensory properties of the eluted fractions of a flavour composition frequently differ considerably from those of the original composition. Following removal of the harmful solvents, the eluted and isolated sensorially active components must be taken up in a harmless solvent and sensorially evaluated by means of dilution analysis. The dilution analysis and the subsequent sensory evaluation are not automated processes. Until now only time-delayed (“off-line”) and relatively complex processes for the separation and tasting of flavour compositions have been described in the prior art.